Mythical crop circles, Stonehenge, California’s Mystery Walls … You don’t have to travel the world to brush paths with some intriguing enigmas. Scattered across Northern California, mysterious walls up to a meter high have long been a source of speculation. Nobody knows who built these stone walls or how they got there; there’s no written documentation … Was it an ancient civilization long forgotten?

California’s oldest Spanish settlers and the Ohlone Native Americans all claim the walls were there long before they arrived. The walls exist in several Bay Area parks, but finding them can be a mystery of its own. Resting just above San Jose, the wild hills of the Sierra Vista Open Space Preserve offer an opportunity for hikers to get up close and personal. Combine the Aquila Loop and Kestrel Trails for a 1.7-mile (round-trip) jaunt that takes you past two portions of the wall ruins.

Head west on the Aquila Loop Trail, and just above a picnic table a small path leads you to a section of boulders. Although the walls have sunk into the ground, you’ll see the rocks have been stacked up in a straight line, forming a portion of an ancient wall. Stretches of the walls are scattered across the countryside. When you finish the loop, head down Kestrel Trail. Sweeping views of San Jose dominate the horizon, and a quarter of a mile down you’ll find another stretch of the mystery wall sloping southeast down the hills. (The wall’s end marks the end of Kestrel Trail.) When you’ve had your fill of pondering these cryptic stones, head back the way you came.

Bonus: For some extra mileage follow the Sierra Vista trail to the Boccardo Loop Trail (3.5-mile round trip). The trail meanders through hillsides, passing through oak woodlands, and opening up to views of the Santa Clara Valley. On a clear day, you can see all the way to San Francisco.

Park at the Kestrel Trailhead on Sierra Rd. The Aquila Loop Trail is just north of the parking lot. Maps are available at the trailhead. No dogs.